1. Field of the Invention
The present invention relates to a circuit, and more specifically relates to a circuit that supplies a voltage outputted from a switching transformer to a target device and a circuit that stabilizes voltage supply to an inverter circuit of an LCD apparatus.
2. Description of the Related Art
Conventionally, if there is a possibility that a voltage to be supplied to a predetermined device will drop, power voltage supply is stabilized by switching among a plurality of power voltage supply lines with a transistor each time a supply voltage drops (as disclosed in Japanese Utility Model Registration Application No. 3110950), or by controlling the on/off of a regulator IC with a microcomputer according to the timing at which supply voltage is switched (as disclosed in Japanese Utility Model Registration Application No. 3120526).
Also known is a technology wherein two lines of power supply are provided and normally power is supplied directly from one of the lines, and when this line causes a drop in power supply or when a large amount of power supply is required, power is supplied, due to a Zener breakdown, from the other line that is connected through a Zener diode connected in reverse direction (as disclosed in Japanese Unexamined Patent Application Publication No. 1998-150723 and Japanese Unexamined Utility Model Registration Application Publication No. 1989-115380).
With the switching power supply lines as described in the Japanese Utility Model Registration Application Nos. 3110950 and 3120526, there were problems such as drops in power supply or difficulty in controlling the timing of line switching. Although it is possible to control the timing for predicted switching as in power on or standby, it is impossible to cope with unexpected power supply drops and the like. Furthermore, to implement the switching it is necessary to add a switching device such as a transistor, which inevitably increases the manufacturing cost.
Also, with the technology of using a regulator as described in the Japanese Unexamined Patent Application Publication No. 1998-150723 and the Japanese Utility Model Registration Application No. 3120526, a large amount of heat is generated and therefore a heat sink or the like must be provided to dispose of unwanted heat. This is disadvantageous in designing the circuit and also the electric power consumed for heat generation is wasted. This heat generation problem also exists in the case of using a Zener diode as described in the Japanese Utility Model Registration Application No. 3120526.